A conventional fuel delivery system includes a fuel tank with a fuel pump located therein for supplying fuel to a plurality of fuel injectors located in a fuel rail. Each fuel injector is controlled by an electronic control unit (ECU) which is responsive to various engine operating conditions to provide a variable pulse width control signal to each injector to meet the fuel demand of the engine. A pressure regulator is interposed between the pump and the rail and is designed to maintain the fuel pressure in the rail at approximately 40 psi greater than engine intake manifold vacuum.
The fuel pump runs at a constant speed and may deliver, for example, 90 liters per hour. Under idle conditions the engine needs only about 3 liters per hour, so in that case 87 liters per hour is returned to the fuel tank from the pressure regulator through return lines. There are a number of problems associated with return of fuel from the high temperature engine area to the relatively low pressure and low temperature which exist in the fuel tank. Because of the high temperature and pressure of the fuel being returned, substantial amounts of fuel vapor are generated and exist in the tank which must be vented to the atmosphere which may in turn create environmental problems.